Avermectins, New Family of Potent Anthelmintic Agents: Producing Organism and Fermentation

TLDR

Avermectins are a chemically related group of macrocyclic lactone derivatives that exhibit extraordinarily potent anthelmintic activity while lacking significant antibacterial or antifungal effects. They are produced by the novel actinomycete Streptomyces avermitilis NRRL 8165, whose distinctive morphological and cultural traits set it apart from other species. The avermectin complex fully inhibited the gastrointestinal nematode *Nematospiroides dubius* in infected mice fed 0.0002 % of the diet for six days, and fermentation optimization raised broth yields from 9 to 500 µg ml⁻¹.

Abstract

The avermectins are a complex of chemically related agents which exhibit extraordinarily potent anthelmintic activity. They are produced by a novel species of actinomycete, NRRL 8165, which we have named Streptomyces avermitilis . The morphological and cultural characteristics which differentiate the producing organism from other species are described. The avermectins have been identified as a series of macrocyclic lactone derivatives which, in contrast to the macrolide or polyene antibiotics, lack significant antibacterial or antifungal activity. The avermectin complex is fully active against the gastrointestinal nematode Nematospiroides dubius when fed to infected mice for 6 days at 0.0002% of the diet. Fermentation development, including medium modification and strain selection, resulted in increasing the broth yields from 9 to 500 μg/ml.